Epoxy resin compositions containing a metal powder, such as aluminum powder, is known. For example, JP-B-50-38606 (the term "JP-B" as used herein means an "examined published Japanese patent application") discloses a resin molding material comprising 100 parts by weight of an epoxy resin, 40 to 60 parts by weight of aluminum powder of 200 to 500 mesh, and 10 to 20 parts by weight of a curing agent, which is molded to provide a resin mold for casting. However, the allowable highest compounding ratio of aluminum powder being 60 parts per 100 parts by weight of an epoxy resin, the resin material considerably shrinks on curing, failing to reproduce a mold faithful to the original. Besides, having a low thermal conductivity, the resin material is liable to undergo distortion on heating. To avoid this, curing must be effected with a slow rise in temperature, achieving poor workability.
JP-A-60-137623 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a method for producing a resin mold for injection molding from an epoxy resin compounded with a relatively large quantity of a metal powder, e.g., aluminum powder or iron powder, as a filler so as to minimize shrinkage on curing and to improve thermal conduction. However, the epoxy resin composition used here comprises a bisphenol A type epoxy resin, as a result, has a high viscosity, and the metal powder to be used as a filler has a relatively large size. Use of large filler particles not only results in production of a resin mold with a poor appearance but also causes separation of the filler due to non-uniform dispersion of the filler in the resin matrix.
Further, JP-A-2-53850 describes a resin material comprising a low-viscosity epoxy resin having a viscosity of not more than 50 poise which contains an alicyclic epoxy resin and not less than 100 parts by weight, per 100 parts by weight of the total weight of the epoxy resin and a curing agent, of a metal powder containing at least 50% by weight of a fine powder having a particle size of not more than 44 .mu.m, the resin material providing a cured product with low shrinkage on curing and high thermal conductivity. The cured product, however, does not satisfy impact resistance.
A resin mold has an advantage of production ease and low cost over a metal mold but, on the other hand, is apt to suffer from cracks during cutting or on repeated use. Accordingly, it has been demanded to develop a resin mold with high strength and small expansion coefficient which is not broken on repeated use. Under the present situation, a resin material providing a resin mold which meets these requirements has not yet been found.